Nuclear hardened liquid crystal display

ABSTRACT

A nuclear hardened liquid crystal display (LCD) and a method for hardening a liquid crystal display is provided. The nuclear hardened LCD can include an LCD glass laminate stack. The LCD glass laminate stack can include a front transparent substrate, a back substrate, and a liquid crystal material disposed between the front transparent substrate and the back substrate. The nuclear hardened LCD can further include a protective laminate stack positioned in front of the LCD glass laminate stack. The protective laminate stack can include a volume absorbing filter, that absorbs selective electromagnetic energy throughout a thickness of the volume absorbing filter.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/531,059 filed Dec. 19, 2003, the disclosure of which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to information display systemsand, more particularly to information display systems hardened to theeffects of electromagnetic energy.

BACKGROUND OF THE INVENTION

One of the most important effects following a nuclear detonation eventis a strong pulse of electromagnetic energy released in very broadfrequency bandwidth. This electromagnetic energy is primarilydistributed as gamma-ray and X-ray radiation; “thermal flash” thatincludes: ultraviolet (UV), visible, and infrared (IR) light;radio-frequency (RF) waves; and electromagnetic pulse (EMP).

Many systems rely on information displays, such as, for example, anactive matrix liquid crystal display (AMLCD). Conventional informationdisplays, however, are susceptible to damage by electromagnetic energy.FIG. 1 depicts a conventional active matrix liquid crystal displaymodule 1. Active matrix liquid crystal display module 1 is positioned infront of a backlight (not shown) and modulates light from the backlightto provide a graphical image to a viewer. Active matrix liquid crystaldisplay module 1 includes a glass laminate stack 11, which contains anelectrically active matrix of pixel elements that are driven by rowdriver circuits 12 and column driver circuits 13 to produce the lightmodulation.

FIG. 2 shows a glass laminate stack 11 of a conventional active matrixliquid crystal display. Glass laminate stack 11 consists of a fronttransparent substrate (also called a front passive plate) 2 facing theviewer and a back substrate (also called a rear active plate) 3positioned in front of a backlight assembly sandwiching a thin layer ofliquid crystal material 15.

FIGS. 3 and 4 show further details of a front transparent substrate 2 ofa conventional active matrix liquid crystal display. A front polarizerfilm 21 (also referred to as an analyzer) covers the viewer-facing sideof the front transparent substrate 2. The opposing side of the fronttransparent substrate 2 is covered in layered sequence from the glasssubstrate by color filters 22 and transparent row electrodes 23.

FIGS. 5 and 6 show further details of a back substrate 3 of aconventional active matrix liquid crystal display. A rear polarizer film31, polarizing light in a sense that is opposite of the front polarizerfilm 21, in the case of normally white conventional active matrix liquidcrystal display, covers the backlight-facing side of back substrate 3.The opposing side of back substrate 3 is covered with active circuitry30 including column electrodes 33 and pixel transistors 34. The activecircuitry 30 is fabricated from silicon structures, such as, amorphoussilicon, polysilicon, and single crystal silicon.

Because AMLCDs absorb a percentage (currently >90%) of light energy,thermal flash radiation from a nuclear detonation can damage informationdisplays by overheating absorbing materials within the informationdisplays, such as, for example, polarizers and color filters. Thermalradiation can also cause liquid crystals to outgas or boil, resulting invoid formation and cell-gap non-uniformity. Gamma radiation and X-raysknock electrons free from atomic nuclei that are struck. In order toprotect an electronic device, electrons that are knocked loose in ashielding layer should be conducted immediately to ground.Electromagnetic pulse (EMP) and electromagnetic interference (EMI)affect information displays through three mechanisms, electric field(E-field), magnetic field (h-field), and radio frequency (RF) coupling.

Challenges hardening AMLCDs arise because conventional methods ofhardening that maximize the absorption of damaging radiation alsosignificantly reduce the display luminance reaching the viewer. Problemsalso arise because conventional shielding mechanisms, such as meshwindows, induce undesirable moiré effects.

Thus, there is a need to overcome these and other problems with theprior art and to provide nuclear hardening methods and apparatus thatmaximize luminance of the display while selectively absorbing damagingradiation.

SUMMARY OF THE INVENTION

According to various embodiments, a nuclear hardened liquid crystaldisplay (LCD) is provided. The nuclear hardened liquid crystal displaycan include an LCD glass laminate stack that includes a fronttransparent substrate, a back substrate, and a liquid crystal materialdisposed between the front transparent substrate and the back substrate.The nuclear hardened liquid crystal display can further include aprotective laminate stack positioned in front of the LCD glass laminatestack, wherein the protective laminate stack includes a volume absorbingfilter that absorbs selective electromagnetic energy.

According to various embodiments, another nuclear hardened liquidcrystal display (LCD) is provided. The nuclear hardened liquid crystaldisplay can include an active matrix liquid crystal display, wherein theactive matrix liquid crystal display comprises a glass laminate stack.The nuclear hardened liquid crystal display can further include abacklight disposed on a back side of the active matrix liquid crystaldisplay, a volume absorbing filter, and a shielding plate. The shieldingplate includes a conductive layer, wherein the shielding plate is atleast one of coated on the volume absorbing filter and coated on asubstrate that is bonded to the volume absorbing filter.

According to various other embodiments, a method for hardening an activematrix liquid display is provided. The method includes positioning athermal volume absorbing material at a front of the active matrix liquiddisplay, wherein a thickness of the thermal volume absorbing material isone millimeter or more. An anti-reflection coating can be provided on aviewer side of the thermal volume absorbing material. A radio frequencyshielding coating can be provided on a backlight side of the thermalvolume absorbing material.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art liquid crystal display (LCD) moduleincluding LCD glass and driver circuits.

FIG. 2 shows a perspective view of the prior art LCD glass of FIG. 1,including a passive plate and an active plate.

FIGS. 3 and 4 illustrate further details of the prior art passive plateof FIG. 2.

FIGS. 5 and 6 illustrate further details of the prior art active plateof FIG. 2.

FIG. 7 shows a perspective view of a nuclear hardened LCD display inaccordance with various embodiments of the present teachings.

FIGS. 8 and 9 illustrate further details of a neutral density plate inaccordance with various embodiments of the present teachings.

FIGS. 10 and 11 illustrate further details of a shielding plate inaccordance with various embodiments of the present teachings.

FIG. 12A illustrates a hardened liquid crystal display (LCD) moduleincluding dual column driver circuits in accordance with variousembodiments of the present teachings.

FIG. 12B illustrates a sectional view of the LCD module of FIG. 12Aalong section line ‘B’ in accordance with various embodiments of thepresent teachings.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to various embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Referring to FIG. 7, a nuclear hardened liquid crystal display (AMLCD)can include several assemblies, such as, for example, a protectivelaminate stack 71, an AMLCD and a backlight chamber 72, and anelectronics chamber 73.

The AMLCD and backlight chamber 72 can include a glass laminate stack11, such as, for example, AMLCD module 1, shown in FIG. 1. Protectivelaminate stack 71 can be positioned in front of, but thermally separatedfrom, glass laminate stack 11. In various embodiments, the thermalseparation can be provided by an air gap 6, although other forms ofthermal separation may be suitable. In various embodiments, the pulseenergy, material specifications, and environmental conditions (e.g.cold-start warmup time) can allow the protective laminate stack to bebonded to the AMLCD. In various embodiments, the protective laminatestack 71 can comprises a volume absorbing filter 4. In variousembodiments, volume absorbing filter 4 can absorb selectiveelectromagnetic energy throughout a thickness of the volume absorbingfilter. For example, volume absorbing filter 4 can absorb selectedspectrum of IR and/or notch in the visible band. According to variousembodiments, volume absorbing filter 4 can transmit a substantialportion of light energy corresponding to at least a red color band, agreen color band, and a blue color band. In various embodiments, volumeabsorbing filter 4 can be a neutral density filter if reduced luminancecan be tolerated.

According to various embodiments, protective laminate can include volumeabsorbing filter 4 on its viewer side (opposing AMLCD glass laminatestack 11) and shielding plate 5 on its backlight side (facing AMLCDglass laminate stack 11). Shielding plate 5 can be a transparentconductive layer, such as, for example, an indium-tin-oxide (ITO) layer.In order to minimize Fresnel reflections, the volume absorbing filter 4can be bonded to the shielding plate 5 using a refractive index matchingadhesive, and the ITO may be optionally index-matched (to air if itfaces the air gap) as well. Because the ITO coating has some absorptionin the thermal flash wavelength band, it, like the volume absorbingfilter 4 can contribute to the thermal flash attenuation. In variousother embodiments, an infrared reflecting film can be added to thestack, thereby preferentially rejecting infrared as opposed to visiblelight.

During a thermal flash event, the AMLCD glass laminate stack 11 willabsorb thermal energy via its color filters 22 (shown in FIG. 4), aswell as obstructions due to the active circuitry 30, including rowlines, column lines 33, thin film transistors 34, storage capacitors,black matrix coatings and the rear polarizer film 31 (shown in FIG. 6).To protect the glass laminate stack, protective laminate stack 71 canfunction as a thermal volume absorbing element that dissipates the flashenergy and heats up more at its viewer facing (front) surface than atits rear surface. This is because more energy per unit area is availableat the proximal surface versus at the distal surface, simply becauseenergy is removed as the flash propagates through the thickness of theprotective laminate stack. The air gap 6 can prevent the thermal energyfrom being conducted to the AMLCD glass laminate stack 11. Due in partto this thermal protection, a commercial off the shelf AMLCD displaymodule 1 (e.g. color filters, polarizers, and liquid crystal) can beincorporated into a hardened display.

In various embodiments, volume absorbing filter 4 and shielding plate 5can be fabricated from glass. In various other embodiments, thermallyshock-resistant borosilicate glass can be used, although other materialsmay be more suitable due to availability, and in such cases, the stackmust be engineered to avoid overstressing. Neutral density glass isavailable from, for example, Schott Corporation (Yonkers, N.Y.).Borosilicate glasses can handle thermal shock better than theirsoda-lime equivalents and are much less expensive than heat conductingsubstrates such as glass-like sapphire. However, one does not alwayshave a choice in the selection of thermal shock aspects of absorbingglass. The protective laminate stack 71 will remove the thermal flashenergy, and in doing-so, will heat-up and slowly dissipate its heat overtime.

According to various embodiments, the shielding plate of the protectivelaminate stack can provide protection against those portions of theelectromagnetic spectrum between 500 kilohertz (kHz) and 400 megahertz(MHz) which are typically referred to as radio frequency (RF) energy.The effect of such RF frequencies on electronic equipment is referred toas electromagnetic interference (EMI). A minimal amount of displayelectronics is located in the AMLCD and backlight compartment 72, alongwith a light source such as stick fluorescent lamps. The remainder ofthe display electronics is contained within the electronics compartment73, which is a separate EMI-shielded enclosure. Nonetheless, thisseparation does not provide a suitable hardened display by itself,because the large area AMLCD glass laminate stack 11 provides a large RFwindow into the backlight compartment 72.

Further details of the volume absorbing filter 4 are shown in FIGS. 8and 9. The viewer-facing side of the neutral density plate 4 can becovered with an antireflective coating 41. The antireflective thin filmcoating 41 in combination with the neutral density substrate can enhancesunlight readability for the display.

In various embodiments, the protective stack 71 can further include apolarizer film 42 aligned to the polarization axis of the AMLCD'sanalyzer 21 (shown in FIG. 3). In various embodiments, polarizer film 42can be lamintated to volume absorbing filter 4 using an opticallytransparent adhesive, of minimal thickness, that can handle hightemperatures. Positioning the substitute polarizer film 42 in front ofthe shielding plate 5 can also result in additional ambient lightrejection. In various embodiments, polarizing film 42 can be a polyvinylalcohol (PVA) layer between two triacetate films (TAC). According tovarious embodiments, the polarizing film can be removed from the glasslaminate stack.

In various embodiments, the volume absorbing filter can becolor-neutral, although some color correction may be available based onthe AMLCD type. Triple-notch and/or electrochromic filter layers can beadded to the volume absorbing filter 4 in various embodiments.

Further details of the shielding plate 5 are shown in FIG. 10. Theviewer facing side of the shielding plate 5 can be coated with acontinuous transparent conductive layer 51. In various embodiments,transparent conductive layer 51 can be indium tin oxide with aresistance of 10-20 ohms per square available from Thin Film Devices(Anaheim, Calif.). The continuous transparent conductive layer 51 can beelectrically bonded around its periphery to the surrounding constructiveenclosure. The combined effect of the shielding plate 5 and the volumeabsorbing filter 4 may reduce the brightness of the light emitted fromthe display by approximately 50%, therefore, a complete hardened AMLCDdisplay unit will require a bright backlight. The indium tin oxidecoating can provide a degree of protection against gamma radiation andX-rays because of the relatively large atomic radii of indium and tinatoms respectively. Should a mesh structure be employed, the thermalflash flux through the aperture of the mesh will be unattenuated, eventhough the average flux leaving the mesh is at a lower level than theincident flux.

According to various embodiments, the materials between the viewer sideof the AMLCD glass laminate stack 11 and polarizer film 42 should notexhibit appreciable birefringence, otherwise color effects may benoticeable.

Referring to FIG. 11, in various embodiments, the backlight-facing sideof the shielding plate 5 can be covered with patterned transparentconductors 52 that are electrically connected at one end only and havethe same effective radio frequency (RF) length as the row electrodes 23,shown in FIG. 4. The patterned transparent conductors 52 can be groundedto provide RF protection.

Referring now to FIGS. 12A and 12B, in various embodiments, the AMLCDglass laminate stack 11 can be cut, exposing the column electrodes 33. Aset of redundant column driver circuits 16 can be added to the liquidcrystal display module 1 and electrically connected to each columnelectrode 33. This can provides additional RF protection by eliminatingthe dipole effect for the RF frequency associated with the length of thecolumn electrode 33, because both ends of each column are now terminatedby Thevinin equivalent to ground.

As shown in the side view of FIG. 12B, the AMLCD glass laminate stack 11can be cut so that the edge of back substrate 3 extends beyond the endof front transparent substrate 2. An edge seal 100 can be applied toprevent liquid crystal material 15 from escaping. The second set ofcolumn driver circuits 16 can be electrically connected to each of thecolumn electrode 33.

In various embodiments, additional layers of indium tin oxide or othertransparent materials known in the art can be added as continuous and/orpatterned coatings. Patterned layers can be configured, for example, toabsorb certain frequencies.

In various other embodiments, a protective laminate stack can be fittedto a projection display. Projection displays have the added concern thatthe projection lens can focus thermal flash energy onto themicro-display, thereby leading to very high power concentrations.According to various embodiments, fold mirrors and projection screenscan be fitted with protective laminate stack as described herein toensure the power density at the micro-display (and any other componentswithin the system) is below damaging levels.

One of ordinary skill in the art understands that other displaytechnologies, both emissive and non-emissive, would also benefit fromthis invention; e.g. electroluminescent, electophoretic, suspendedparticle, field emissive display, plasma display, and any otherelectro-optical medium. For displays/materials having unknownabsorptance characteristics, measurements can be made at the OpticalMeasurements Facility (OMF) in the Materials and ManufacturingDirectorate of the Air Force Research Laboratory (Wright-Patterson AirForce Base, Ohio). Of significant importance is the ability to measurethese characteristics at all relavant wavelengths, and at all angles ofincendence, since the angle between the energy from the thermal flashand display-normal is random.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A nuclear hardened liquid crystal display (LCD) comprising: an LCDglass laminate stack, wherein the LCD glass laminate stack comprises, afront transparent substrate, a back substrate, and a liquid crystalmaterial disposed between the front transparent substrate and the backsubstrate; and a protective laminate stack positioned in front of theLCD glass laminate stack, wherein the protective laminate stackcomprises a volume absorbing filter that absorbs selectiveelectromagnetic energy.
 2. The display of claim 1, wherein the volumeabsorbing filter absorbs energy in an infrared portion of theelectromagnetic spectrum.
 3. The display of claim 1, wherein the volumeabsorbing filter transmits a substantial portion of light energycorresponding to at least a red color band, a green color band, and ablue color band.
 4. The display of claim 1, wherein the protectivelaminate stack further comprises a polarizing filter.
 5. The display ofclaim 1, wherein the protective laminate stack further comprises atransparent conductive layer, wherein said conductive layer is grounded.6. The display of claim 1, wherein the protective laminate stack furthercomprises an anti-reflective layer.
 7. The nuclear hardened LCD of claim1, further comprising an infrared reflecting film.